The physical and mechanical properties of foams make them useful for a wide variety of applications, including insulation, upholstery and bedding. However, many foams, for example polyurethane, are inherently flammable and lead to melting and spread of burning debris. In the case of many "conventional" foams such characteristics lead to the sustaining of combustion by progressive smoldering even after the actual flames have extinguished.
It is considered that cellular materials manufactured from flammable polymers are more flammable than the solid materials because the insulating effect of their cellular nature allows a rapid build-up of heat at the heating surface with a consequence high rate of pyrolysis. In solid materials this heat build-up is at a lower rate because of the higher conductivity of the solid material. Although rigid foams have similar thermal conductivity behavior to flexible foams, the high cross-linked nature of their chemical structure makes them less flammable as polymers and also inherently more inclined to form a protective char rather than to form the flaming molten polymer droplets which occur with flexible foams. While both solid and rigid cellular materials burn less easily than flexible foams and are easier to extinguish, they tend to smolder and emit toxic fumes.
Various methods are known to reduce the flammability of polymer foams. Commonly, additives such as aluminum trihydrate or phosphorus-containing compounds are incorporated into the foam for this purpose. Alternatively, halogenated polyols, especially brominated polyols such as dibromoneopentyl glycol, or mod acrylics are used in connection with polyurethanes to increase the flame resistance of the foam. None of these additives have proved entirely satisfactory.
It is known that the incorporation of trimerized polyisocyanates (i.e. isocyanaurates) into a polyurethane foam improves its burn characteristics. For example, trimerized toluenediisocyanate has been used to prepare flexible foams. Although these foams do exhibit good foam characteristics, they also have poor physical properties, particularly poor compression sets and partial cell collapse In addition, trimerized toluene diisocyanate tends to precipitate from the isocyanate solution in which it is dissolved, causing storage problems and a lack of uniformity in foams prepared therewith.
Polyurethane foams have heretofore been rendered electroconductive by impregnating the foam with an aqueous dispersion of conductive carbon black containing a binder, by impregnating the foam with a styrene butadiene binder containing conductive carbon, by wetting polyurethane foam particles with binders and conductive carbon black and then molding to a desired configuration or by adding conductive carbon black to the polyurethane prepolymer and then foaming.
U.S. Pat. No. 4,698,369 to Bell discloses flexible, flame-retardant polyurethane foams containing up to 30% graphite.
U.S. Pat. No. 4,489,913 to Gurgiolo et al, which is herein incorporated by reference, relates to electroconductive foams prepared by dehydrohalogenating a foam containing a halogen-containing polymer including chlorinated polyacrylonitrile.
U.S. Pat. No. 4,832,881 to Arnold, Jr. et al discloses the preparation of low density microcellular carbon foams. However, the foams are rigid and brittle and possess a specific resistivity of less than 10.sup.1 ohm-cm.
U.S. Pat. No. 4,837,076 to McCullough, Jr. et al, which is herein incorporated by reference, relates to the preparation of non-linear carbonaceous fibers and to carbonaceous fibers having different electroconductivity.
The term "stabilized" herein applies to precursor foams which have been oxidized at specific temperature, typically about 150-525.degree. C., preferably less than about 250.degree. C. as described in said U.S. Pat. No. 4,837,076. It will be understood that in some instances the foams are oxidized by chemical oxidants at lower temperatures.
The term "material density" as used herein refers to the density of the material as measured on a standard density gradient column according to the procedure described by David M. Hall in "Practical Fiber Identification", Dept. of Textile Engineering, Auburn Un., 2d Ed., 1982, p. 51-54.
The carbonaceous fibers have an LOI value greater than 40 as tested according to ASTM D2863-77. The test method is also known as "Oxygen Index" or "Limited Oxygen Index" (LOI). With this procedure, the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is determined at which a vertically mounted specimen is ignited at its upper end and just (barely) continues to burn. The width of the specimen is from 0.65 to 0.3 cm with a length of from 7 to 15 cm. The LOI value is calculated according to the equation: ##EQU1##
The term "carbonaceous foams" as used herein relates to polymeric foams whose carbon content has been irreversibly increased as a result of a chemical reaction such as a heat treatment, as disclosed in U.S. Pat. No. 4,837,076.
The term "non-graphitic" as used herein relates to those carbonaceous materials having an elemental carbon content of less than 92 percent (%), which are substantially free of oriented carbon or graphite microcrystals of a three dimensional order, and as further defined in U.S. Pat. No. 4,005,183, which is herein incorporated by reference.